Accounting For Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Disclosure [Abstract]
Federal income taxes at statutory rates	$ 42,021	$ 56,060	$ 51,137
Tax effect of regulatory treatment of utility plant differences	2,432	1,798	2,761
State income tax expense	985	687	624
Settlement of prior year tax returns and adjustment of tax reserves	(2,198)	163	(1,030)
Manufacturing deduction	(1,100)	(1,099)	(1,630)
Other	(879)	(977)	(705)
Total income tax expense	$ 41,261	$ 56,632	$ 51,157